1. Field of the Invention
The present invention relates to an electric power conversion apparatus for charging a power storage unit with a generated electric power received from an electric power generation source, a power storage system, and an power storage method.
2. Description of the Related Art
An electric power conversion apparatus that converts and obtains a generated electric power received from an electric power generation source (for example, an electric power generation source such as photovoltaics including a solar battery using natural energy) is known in the related art (refer to Japanese Unexamined Patent Application Publication No. 9-135575). An electric power conversion apparatus that charges a power storage unit (for example, a storage battery) with the obtained electric power is also known in the related art (refer to Japanese Unexamined Patent Application Publication No. 2004-120950).
In such electric power conversion apparatus, it is important to efficiently charge the power storage unit with the generated electric power received from the electric power generation source. For example, in Japanese Unexamined Patent Application Publication No. 2007-104810, an electric power conversion apparatus is disclosed that can prevent deterioration in charging efficiency.
FIGS. 8A and 8B are circuit diagrams for describing the electric power conversion apparatus A disclosed in Japanese Unexamined Patent Application Publication No. 2007-104810. FIG. 8A illustrates a circuit configuration of an entire power storage system C disclosed in Japanese Unexamined Patent Application Publication No. 2007-104810. FIG. 8B illustrates a circuit configuration of a control unit A1 and a DC-DC converter A2 of the electric power conversion apparatus A in the power storage system C.
The electric power conversion apparatus A in Japanese Unexamined Patent Application Publication No. 2007-104810 illustrated in FIGS. 8A and 8B charges a power storage unit B2 with a generated electric power Eg received from an electric power generation source B1 and includes a control unit A1, a DC-DC converter A2 including a switching element A3 and a Schottky diode A4 (refer to FIG. 8B), and a Schottky diode A5. The electric power conversion apparatus A has a configuration that converts the generated electric power Eg into a pulse-like boosted electric power, rectifies it with the Schottky diode A4 (refer to FIG. 8B) that operates as a first rectifying unit, and thus generates a first boosted electric power. In addition, the electric power conversion apparatus A maintains operation at a second boosted electric power obtained by rectifying the pulse-like boosted electric power using the Schottky diode A5 (refer to FIG. 8A) that operates as a second rectifying unit.
The power conversion apparatus A disclosed in Japanese Unexamined Patent Application Publication No. 2007-104810 has a circuit configuration in which the operation is maintained at the second boosted electric power obtained by rectifying the first boosted electric power using the Schottky diode A5 and if the power storage unit B2 is not charged, an amount of energy stored in the power storage unit B2 is prevented from being consumed. However, an electric power necessary for electric power conversion operation by the DC-DC converter A2 can be supplied only from the electric power generation source B1 side. Because of this, for example, although the electric power generation source B1 generates the electric power Eg (the generated electric power greater than the electric power necessary for the power conversion operation by the DC-DC converter A2) with which the power storage unit B2 can be charged, if the generated power voltage Vg fails to reach the voltage to be given to the control unit A1, which is necessary for the electric power conversion operation by the DC-DC converter A2, the control unit A1 may not operate the DC-DC converter A2. Thus, although the electric power Eg with which the power storage unit B2 can be charged is generated, the charging may not be performed on the power storage unit B2. This brings about a disadvantage that the generated electric power Eg becomes useless, and thus the efficiency with which the charging can be performed is decreased as much as the generated electric power Eg is useless.